We propose to develop a table-top sized spectroscopic method to quantify 14C in milligram sized biological samples at levels down to the natural isotopic abundance, using a technique called Cavity Ring Down Spectroscopy. This system will be much cheaper to acquire and to operate, and could eventually replace the current state of the art technology -- accelerator mass spectrometry. This approach will lead to a new paradigm for 14C analysis in allowing studies to be carried out on the metabolism, disposition, fate and mass balance of 14C-labeled therapeutic entities for drug development, potential toxicants for risk assessment, and analysis of biomarkers for personalized medicine. Given the expected cost and simplicity of operation, this new technique will enable much greater access to high sensitivity 14C analysis than now currently available as any biomedical or biochemistry laboratory could afford to operate such an instrument.